Operators of both military and civilian aircraft constantly endeavor to reduce the expenses associated with use of the aircraft. Since fuel consumption represents a significant portion of an aircraft's operating expenses, improved fuel efficiency is a persistent goal. To that end, it has been observed that jet engines are most propulsively efficient when a large mass of air is accelerated at a modest rate (contrasted with the fuel consumption experienced when a lower volume of air undergoes significant acceleration).
One technique for increasing the volume of propulsive air is to employ a turbofan configuration of the jet engine. In a turbofan configuration, a core portion includes a compressor, fuel injection means, and turbine. A quantity of the air entering the engine's inlet is introduced into the core and is subsequently compressed, fueled, and combusted. Another portion of the air entering the inlet bypasses the core and this relatively dense air is joined with the combusted airflow aft of the jet engine. The ratio between the mass flow rate of air that bypasses the engine core (un-combusted air) to the mass flow rate passing through the engine core that is involved in combustion, may be referred to as the bypass ratio (BPR).
While this technique is effective at increasing fuel efficiency, it necessitates a larger diameter engine that has diminished thrust capacity when compared with a low BPR or pure turbojet configuration (particularly at higher airframe speeds).
Efficiency also suffers from resulting pressure drag at the location of flow separation near the top of an airfoil near the leading edge (i.e., the boundary region), the size of the engine nacelle, and wake turbulence. While techniques have been previously employed to mitigate these sources of inefficiency, traditional remedial measures have focused on piecemeal resolution of the aforementioned sources of drag.
Therefore, a need exists for apparatus and methods of improving jet engine fuel efficiency by production of high volume propulsive airflow, while mitigating a plurality of drag sources.